This invention relates generally to sod harvesters.
Sod harvesters have been commercially available for a long time, and usually are designed as self-propelled machines or as a cutting unit which can be attached to a conventional tractor. In either case, the harvester has a cutting head which includes (a) a generally-horizontal knife to undercut the sod at a specified depth, (b) side cutting blades or coulters to cut the edges of the sod strip, and (c) a roller to support the weight of the cutting head and to establish the thickness of the sod strip. Cut strips of sod are delivered onto a conveyor which conveys the strips rearwardly and upwardly away from the cutting head, for collection.
Sod harvesters have used a variety of methods to follow the contour of the ground; in general, the objective is to allow the operator to cut a thin strip of sod without the risk of scalping, or cutting too thinly on occasion. Some harvesters, commonly referred to as xe2x80x9cconventionalxe2x80x9d or xe2x80x9cfixed headxe2x80x9d harvesters, have the cutting head rigidly connected to the conveyor frame. Examples of this type of harvester are the harvester described in U.S. Pat. No. 3,540,535, the Brouwer model 1555, and the Kesmac model 2100. These harvesters include a pivoting xe2x80x9cball jointxe2x80x9d connection at the rear of the conveyor, which allows the cutting head to rise and fall with undulations in the direction of motion of the harvester. A xe2x80x9ctrack rodxe2x80x9d connects the cutting head or conveyor to the tractor with pivoting ball joints and holds the cutting head parallel to the direction of motion. These pivot joints also allow the conveyor and cutting head frame to rock from side to side to follow undulations perpendicular to the direction of motion of the harvester. The axis about which the conveyor and cutter assembly rotates is defined by the location of the centres of the rear pivot point and the track rod connection to the cutting head or conveyor. Since this axis is not horizontal, the cutting knives turn away from being exactly perpendicular to the direction of travel when the head pivots, resulting in damage to the edges of the sod strip.
This problem is addressed by harvesters that are commonly referred to as xe2x80x9cfloating headxe2x80x9d, or xe2x80x9cpivoting headxe2x80x9d, harvesters, which have a pivoting connection between the cutting head frame and the conveyor frame. U.S. Pat. Nos. 4,621,696, 3,807,504, and 4,892,152 disclose harvesters of this type, in which the cutting head can tilt about a horizontal pivot axis. The cutting knives and roller no longer pivot front-to-back. However, since the axis of tilt lies at some distance above ground level, the cutting head can be induced to pivot by a side load on the knives and roller, such as would happen if sod is being cut on a curve, as is common with center-pivot irrigation sod cultivation. This can result in scalping.
One attempt to solve the floating head problem is disclosed in U.S. Pat. No. 6,112,825. This patent describes a floating head design in which the pivoting connection between the cutting head and the conveyor is angled, such that the pivot axis intersects the knife. It should be noted, however, that a side load on the knives and roller can induce the whole assembly to pivot on an axis defined by the front and rear support ball joints, causing scalping.
An object of the present invention is to provide improvements intended to address the problems of prior art sod harvesters. In particular, the invention provides an improved manner of mounting the cutting head to the conveyor to control uniformity in the thickness of sod strips being harvested.
The sod harvester of the invention includes a drive unit for moving the harvester in a forward direction, a cutting head for cutting a strip of sod from the ground as the harvester moves in said forward direction, and conveyor means disposed rearwardly of the cutting head for receiving cut strips of sod from the cutting head and conveying the strips rearwardly for collection. The invention provides means for connecting the conveyor and the cutting head, comprising a ball joint disposed on a longitudinal centre line of the cutting head and a pair of laterally spaced links, each connected at one end to the conveyor means and at the opposite end to the cutting head at respective connection points that are selected to constrain the cutting head laterally with respect to the conveyor means, while permitting lateral tilting of the cutting head about the ball joint to accommodate lateral unevenness in the ground.
In other words, the invention provides an improved means of connecting the cutting head and the conveyor to allow free flotation of the ground-following roller and cutting knives, with substantially reduced scalping and damage to edges of the sod strip.
Preferably, the conveyor is pivotally mounted so that its leading end can move up and down to follow ground contours, but is constrained from side to side movement, as in most floating head harvesters. The ball joint is located below the conveyor and behind the cutting head, and the two links are to the outside of the conveyor, located at a distance vertically from the ball joint. The links constrain the cutting head to remain perpendicular to the direction of travel, while at the same time allowing it to rock from side to side in response to changes in ground contour.
This mounting arrangement does not create a discrete axis about which the cutting heat pivots in relation to the conveyor frame. A notional pivot axis can be defined as an axis that intersects the center ball joint, is oriented in the direction of travel, and is angled downward at the same angle as the two links in their centre positions (cutting head horizontal). The actual rocking of the cutting head will deviate from this notional axis to the extent that the ends of the links connected to the cutting head frame deviate from a plane normal to the notional axis as the cutting head rocks. With the notional axis oriented to approximately the bottom of the ground-following roller, substantially less xe2x80x9cinduced pivotingxe2x80x9d is experienced relative to prior floating heads.
An advantage of the preferred embodiment of the invention over a single pivot shaft between the cutting head frame and the conveyor frame is that it permits greater ground clearance.
A further advantage is that adjustable links provide a means of adjusting the vertical distance between the back of a xe2x80x9csod guidexe2x80x9d that is usually provided at the rear of the cutting head to the leading end of the conveyor. As the links are shortened, the sod guide moves up relative to the conveyor. This relationship is important to the smooth and gentle transfer of sod from the cutting blade to the conveyor. Prior art sod harvesters have no way of adjusting that relationship without changing the depth of cut.